I'd say 'extension' not 'appropriation'. It would probably have been one of the few days when workers had a holiday and it goes back to the Jacks-in-the-Green, who were Victorian chimney sweeps who wanted a way to get some money at a time of year when work was short.

May Day has always been a 'common people's' holiday rather than a church festival (remember the scene in Tess of the D'Urbervilles?)so it seems right that it turned into a way of celebrating the rights of the common people.